The goal of the proposed project is the molecular definition of velo- cardio-facial syndrome (VCFS) and DiGeorge Syndrome (DGS). VCFS was first described by our collaborator, Dr. Robert Shprintzen, and the affected children usually have cleft palate, pharyngeal insufficiency and conotruncal heart abnormalities. In addition, some patients are mentally retarded and exhibit retarded growth, thymic hypoplasia or aplasia, hypoparathyroidism and as they grow they may develop behavioral abnormalities. The organ systems involved and the pattern of abnormalities suggest that VCFS and DGS are the result of a developmental field defect and involves abnormalities in neural crest migration. The precise molecular basis for these disorders, however, is not understood. Several studies including our own have shown that a very large proportion, if not all, of the VCFS and DGS patients are hemizygous for a part of chromosome 22. It is therefore possible that the reduced dosage of one or more gene products encoded by the DNA encompassed by the deletions play a key role in the etiology of these disorders. We propose a multifaceted program to deduce the molecular basis for VCFS and DGS etiology. The goal is to isolate the gene(s) which is responsible for the phenotypic spectrum associated with these syndromes. We propose to achieve this goal by constructing a physical map of the human chromosome 22q11 region in the form of an overlapping yeast artificial chromosome (YAC) contig and isolate genes which are located in the region which is commonly deleted in patients. We have developed a number of molecular markers which are known to be deleted in VCFS patients and identified several YACs that contain these markers. The YACs will be assembled into contigs which will define the physical map of 22q11 and we will derive highly polymorphic chromosome 22 specific markers from these YACs. We will define the smallest region of 22q11 which is consistently deleted in patients (critical region) by examining the DNA from a large number of patients and their parents with the highly polymorphic markers. It is currently estimated that the size of the critical region is less than 700 kb and the probes we propose to use would have a resolution to detect deletions as small as 100-200 kb. One or two YACs which define the critical region will be utilized to isolate cDNAs encoded by genes in them. The cDNAs will be obtained by an affinity hybridization approach developed by us using short fragment cDNA libraries derived from total human fetus, human fetal and adult brain and testes. The cDNA fragments will be converted into full length cDNAs and utilized to examine their developmental patterns of expression in the mouse. Identification of a gene(s) that is located in the critical region and expressed at the appropriate developmental stage will be a lead candidate for VCFS and DGS etiology due to haploinsufficiency.